1. Field of the Invention
The present invention relates to a camera unit for driving lenses by an electrostatic actuator and to a method of manufacturing the camera unit, and more particularly to a camera unit and a method of manufacturing the same by which an assembling accuracy can be improved.
2. Description of the Related Art
There are camera units using an electrostatic actuator as a small actuator. In this camera unit, an image pickup device is mounted on a substrate as well as a stator of the electrostatic actuator is attached to the substrate through a lens holder.
FIG. 10 is a perspective view, partly in cross section, of an ordinary camera unit 100, and FIG. 11 is an exploded perspective view showing the camera unit 100. In these figures, arrows X, Y, Z show three directions perpendicular to each other, and, in particular, the arrow X shows the moving direction of first and second movable units 140 and 150.
The camera unit 100 includes an image pickup device unit 110 and a zoom lens unit 120. The image pickup device unit 110 includes a substrate 111, and a sensor 112 such as a CCD or the like and an electronic part 113 such as a switching device or the like, which are disposed on the substrate 111.
The zoom lens unit 120 includes a cylindrical cover 121, a stationary unit 130, a first movable unit 140, and a second movable unit 150. The first and second movable units 140 and 150 are inserted into a stationary unit frame 131 (which will be described later) such that they can be moved along an optical direction C while being separated from each other.
The stationary unit 130 includes the stationary unit frame 131 composed of a hollow frame member having a passing-though portion and formed in a cuboid shape. Attached to the stationary unit frame 131 are a driving electrode substrate 132 for driving the first and second movable units 140 and 150 and a holding electrode substrate 133 for holding the first and second movable units 140 and 150 at the positions thereof. An electrostatic actuator is composed of the stationary unit 130 and the movable units 140 and 150.
Stationary unit electrodes 132a and 133a each composed of a plurality of electrodes are formed on the surfaces of the driving electrode substrate 132 and the holding electrode substrate 133, respectively and execute driving operation or a holding operation in response to a signal from the electronic part 113. At the time, a voltage applied to the stationary unit electrodes 132a and 133a has a relatively high voltage level of at least 100 V. This is because since the force generated by the electrostatic actuator is proportional to the square of an applied voltage, a high voltage is necessary to generate a large force. The voltage applied to the stationary unit electrodes 132a and 133a is created by boosting a low voltage (for example, 1.5 V, 1.8 V, 2.5 V, etc.).
The thus created high voltage is formed in voltage waveform patterns with respect to channels as many as the plurality of electrodes of the stationary unit electrode by the electronic part 113 disposed on the substrate 111 of the camera unit 100, each of the voltage waveform patterns being predetermined as to each of the channels. The thus formed voltage waveforms are applied between the stationary unit electrodes 132a and 133a of the stationary unit 130 and the first and second movable units 140 and 150, and the first and second movable units 140 and 150 are driven by an electrostatic attracting force (coulomb force) generated between both the electrodes.
The camera unit using the electrostatic actuator described above has the following problems. That is, when the camera unit is composed of the electrostatic actuator and the image pickup device, the electrostatic actuator is attached to the image pickup device through an actuator attachment holder in many cases. In this case, when a lens holder is attached to a substrate with a bad accuracy, the image pickup device becomes misaligned with the optical axis of a movable lens in the actuator. Accordingly, a problem arises in that image quality is deteriorated. Otherwise, since the electrostatic actuator is attached to the image pickup device through the actuator attachment holder, the image pickup device and the electrostatic actuator cannot be effectively disposed. Further, a problem also arises in that productivity is decreased by an increase in the number of assembly processes.
In contrast, when the electrostatic actuator is simultaneously used together with another electronic device, a problem arises in that electro magnetic interference (EMI) occurs. That is, this is a problem of radiation noise generated from a circuit portion located forward of a switching device because the waveform patterns are created from the high voltage supplied to the electrostatic actuator. Counter-measures often employed to solve this problem are to insert a capacitor for lowering the peak of the noise or to shield a source, which is assumed to generate noise, with a metal. However, these countermeasures are time consuming and increase cost and further prevent reduction in size of the camera unit.
The camera unit may be mounted on a mobile phone, PDA, and the like, and, in this case, the space in which the camera is installed may be strictly restricted. Since there is an increasing demand for a small camera unit, a technology for reducing the size of a camera unit is a very important. Note that there is known a technology for reducing the thickness of a camera unit by mounting an image pickup device on an FPC member (refer to public documents 1 and 2).